Film-forming structure on work and film-forming method on work

ABSTRACT

A film-forming structure and a film-forming method on a work include closely depositing a thin primary film on a work, the primary film being a suboxide or an oxide including metal and is soft and has insulation properties and corrosion resistance. The primary film is porous film. The work is integrated with the primary film to prevent the primary film from peeling, and thereby improving the workability. The thin secondary film such as a coating is attached to the primary film closely, thereby reducing the amount of paint used. The primary film is integrated with the secondary film to prevent the secondary film from peeling, improving the workability after formation of the secondary film, and thereby forming the primary and secondary films rationally.

TECHNICAL FIELD

The present invention relates to a film-forming structure and a film-forming method on a work that include closely depositing a thin primary film on a work, the primary film being a suboxide or an oxide which is soft and has insulation properties and corrosion resistance. The work is integrated with the primary film to prevent the primary film from peeling, and thereby improving the workability. A thin secondary film such as a coating is attached to the primary film closely, thereby reducing the amount of paint used. The primary film is integrated with the secondary film to prevent the secondary film from peeling and cracking, improving the workability after formation of the secondary film, and thereby forming the primary and secondary films rationally.

BACKGROUND ART

Since plating is a metal film, pinholes generated by electrolysis are unavoidable, and thus leading to a problem of corrosion due to potential difference in different metals. In coating, since rust on metal surfaces generated by oxygen permeation is unavoidable, thick coatings are formed to deal with the problem. Thus, a needs exits for an improved surface treatment which utilizes the advantages and covers the shortcomings of plating and coating.

In order to deal with such needs, for example, there is a coated steel plate in which a hot-dipped steel plate including aluminum is heated before coating, the surface to be coated is conditioned, for example, by chromating, a primer coating is applied to the surface to have a thickness of 2 to 15 μm, and a top coating is applied thereon to have a thickness of 5 to 30 μm (refer, for example, to Patent Document 1).

However, the above coated steel plate needs to be conditioned by subjecting the coating surface to a chemical conversion treatment before coating. Then the primer coating and the top coating are required, which leads to a time consuming process. Further, since the coating becomes thick, it tends to peel off, which leads to peeling and cracking during a subsequent processing. Thus, the coated steel plate has a poor workability.

Since forming a uniform chromate film is difficult, a surface conditioning is required, in which an acid surface conditioner is applied to an original plate for coating before a chromate treatment. This leads to a time-consuming process. Further, the oxide on the top surface layer of plating is etched by the surface conditioner, so that corrosion resistance of the interface between the surface layer of the plated layer and the primer coating of the original plate for coating is decreased.

To solve the above problems, a method is provided in which magnesium ions are contained in the surface conditioner beforehand, the conditioned surface of the plated layer is further conditioned with an acid aqueous solution including magnesium, and magnesium is replaced and deposited to prevent corrosion of the interface between the surface layer of the plated layer and the primer coating of the coated original plate (refer, for example, to Patent Document 2).

However, the above method can only be applied to certain types of hot-dipped galvanized steel plate. Surface condition of the coated original plate is too complicated, which also makes preparation of the surface conditioner complicated. Further, the coating process is still complicated, unproductive, and inefficient.

In order to deal with such needs, the other surface treatment method is provided, in which a chromium plating and a chromium oxide are deposited in separate processes, metal chromium is actively deposited to couple with the chromium oxide in the chemical treatment bath, a high coulomb treatment is performed at high current density in the chemical treatment bath, ferrous ions are contained in the chemical treatment bath of a chromic anhydride alone to attach a coating on the surface of the chromium-plated steel plate (refer, for example, to Patent Document 3).

However, the above method takes time for treatment since the chromium plating and the chromium oxide are deposited separately. Further, since metal chromium is actively deposited to couple with the chromium oxide, conductivity of the chromium oxide is promoted, and the hardness is increased. Thus, corrosion due to potential difference between the chromium oxide and chromium steel plate tends to occur. Further, the increase in hardness of the chromium oxide leads to a poor workability after formation of the film. When the coated product is bent, the coating tends to peel off and crack.

CITATION LIST Patent Document [Patent Document 1] JP-A-2002-248415 [Patent Document 2] JP-A-2003-171779 [Patent Document 3] JP-A-57-35699 SUMMARY OF INVENTION Technical Problem

The present invention addresses such problems and aims to provide a film-forming structure and a film-forming method on a work that include closely depositing a thin primary film on a work, the primary film being a suboxide or an oxide which is soft and has insulation properties and corrosion resistance. The work is integrated with the primary film to prevent the primary film from peeling, and thereby improving the workability. The thin secondary film such as a coating is attached to the primary film closely, thereby reducing the amount of paint used. The primary film is integrated with the secondary film to prevent the secondary film from peeling and cracking, improving the workability after formation of the secondary film, and thereby forming the primary and secondary films rationally.

Solution to Problem

According to a first aspect of the invention, a film forming structure on a work includes a work having a surface on which a film is formed; a thin primary film formed by a suboxide or an oxide including metal, deposited on the surface of the work, and wherein the primary film is a porous film. Accordingly, the primary film becomes thinner and softer, improving insulation properties and corrosion resistance. Additionally, the suboxide is combined with oxygen in the air to form a rigid oxide film, the secondary film is formed on the primary film more easily, improving the adhesion between the primary film and the secondary film. Further, the films is prevented from peeling and cracking.

A second aspect of the invention includes an impregnation layer formed by the primary film on the surface of the work. Accordingly, the work is integral with the primary film on the surface layer of the work, preventing the primary film from peeling and cracking. The porous structure of the primary film enables the secondary film to be adhered firmly and rigidly, and thereby preventing peeling.

According to a third aspect of the invention, the primary film has a surface having minute irregularities. Accordingly, adhesion of the secondary film to the primary film can be improved. Further, when a coating which is the secondary film is formed on the primary film, for example, the primary film functions instead of primers that have been frequently used, and thus forming the coating rationally.

According to a fourth aspect of the invention, the suboxide is a chromium suboxide, and the oxide is a chromium oxide. Accordingly, the surface of the film is formed with minute irregularities, and thus improving adhesion of the secondary film.

According to a fifth aspect of the invention, the primary film is softer than metal chromium and has insulation properties and corrosion resistance. Accordingly, the primary film, which is lighter than metal chromium, has an improved workability, insulation properties and corrosion resistance.

A sixth aspect of the invention includes a thin secondary film formed on the surface with the irregularities of the primary film. Accordingly, the secondary film is formed on the primary film having a porous structure firmly and rigidly, preventing the secondary film from peeling and cracking. Further, workability of the work after formation of the secondary film is improved.

A seventh aspect of the invention includes an impregnation layer formed by the secondary film on a surface layer of the primary film. Accordingly, the primary film is integral with the secondary film, preventing the secondary film from peeling and cracking. The porous structure of the primary film makes the secondary film to be adhered firmly and rigidly.

According to an eighth aspect of the invention, fine particles or crystals of the secondary film are disposed on the irregularities of the primary film independently and with high density. Accordingly, when a stress is applied to a part of the fine particles and crystals of the secondary film, the rest of the fine particles and crystals is not affected. Thus, when the work is bent or the surface of the secondary film is damaged after formation of the secondary film, peeling or cracking of the secondary film does not occur. With the improved workability of the work, various processing techniques can be applied to the work.

According to a ninth aspect of the invention, the primary film has a thickness of 1 μm or more and the secondary film has a thickness of 5 μm or more. Accordingly, the thinner primary and secondary films are formed. When the secondary film such as a coating is formed, the primary film is allowed to function for rationalization instead of conventional primers. Additionally, by forming the thinner secondary film, less paint is used, for example, the secondary film such as a coating is formed rationally and at low cost.

According to a tenth aspect of the invention, the secondary film includes any one of a polymer material, an inorganic or organic paint coating, a functional material, or ceramics. Accordingly, various materials may be used for the secondary film.

According to an eleventh aspect of the invention, the work is any one of stainless steel, nickel, iron, copper, aluminum, brass, other metals, alloy, synthetic resin, glass, ceramics, paper, fiber, or wood. Accordingly, various materials may be used.

According to a twelfth aspect of the invention, a film-forming method on a work for forming the film on the surface of the work includes: placing the work and an anode piece in a bath for receiving a treatment liquid; applying positive and negative voltages for the work and the anode piece; adjusting a bath temperature of the treatment liquid to low temperature; and depositing a thin and porous primary film formed by a suboxide or an oxide containing metal ions in the treatment liquid on the work by electrochemical action, or depositing a thin and porous primary film formed by a suboxide or an oxide containing metal ions in the treatment liquid in an electroless bath on the work by chemical reaction. Accordingly, in the case of the electrochemical action, deposition of the suboxide or oxide on the work is promoted, deposition of metal chromium is inhibited, and thus making the suboxide or oxide softer than the metal chromium. Further, the primary film is formed on the surface layer of the work firmly and rigidly and prevented from peeling and cracking, and thus the workability is improved. In the case of the chemical reaction, the primary film is formed more easily with simple facilities compared with a case of electrochemical action.

According to a thirteenth aspect of the invention, the treatment liquid of the electrochemical action includes chromic anhydride and a reduction inhibitor. Accordingly, dispersion of chromate is achieved during electrolysis of the treatment liquid, while a current which passes through the work is inhibited, and thereby inhibiting deposition of metal chromium and inhibiting the conductivity and the hardness of the primary film.

According to a fourteenth aspect of the invention, the treatment liquid of the chemical action includes an agent for supplying metal ions, a reducing agent, and an additive such as ceramics. Accordingly, deposition of the additive which is the suboxide or oxide, such as ceramics, is promoted.

According to a fifteenth aspect of the invention, a bath temperature of the treatment liquid of the electrochemical action is adjusted to 10° C. or less. Accordingly, deposition of the primary film is promoted and deposition of the metal chromium is inhibited, and thereby promoting deposition of the chromium suboxide.

A sixteenth aspect of the invention includes a thin secondary film, wherein the secondary film is attached to or adsorbed on the primary film, or the secondary film is formed by impregnation or firing. Accordingly, the secondary film such as a coating is formed firmly and rigidly on the porous primary film.

According to a seventeenth aspect of the invention, the secondary film includes any one of a polymer material, an inorganic or organic paint coating, a functional material, or ceramics, and any one of the above is applied, sprayed, or baked on the primary film, or the work including the primary film is immersed into one of the materials above described, or applying a voltage or an electric field to the work including the paint and the primary film, or the ceramics are fired. Accordingly, the secondary film of the above materials is attached to or adsorbed on the primary film, or the secondary film is formed by impregnation or firing.

Advantageous Effects of Invention

According to a first aspect of the invention, a thin primary film formed by a suboxide or an oxide including metal is deposited on the surface of the work, and wherein the primary film is a porous film. Accordingly, the primary film becomes thinner and softer, improving insulation properties and corrosion resistance. Additionally, the suboxide is combined with oxygen in the air to form a rigid oxide film, the secondary film is formed on the primary film more easily, improving the adhesion between the primary film and the secondary film. Further, the films can be prevented from peeling and cracking.

A second aspect of the invention includes an impregnation layer formed by the primary film on the surface of the work. Accordingly, the work is integral with the primary film on the surface layer of the work, preventing the primary film from peeling and cracking. The porous structure of the primary film enables the secondary film to be adhered firmly and rigidly, and thereby preventing peeling.

According to a third aspect of the invention, the primary film has a surface having minute irregularities. Accordingly, adhesion of the secondary film to the primary film can be improved. Further, when a coating which is the secondary film is formed on the primary film, for example, the primary film functions instead of primers that have been frequently used, and thus forming the coating rationally.

According to a fourth aspect of the invention, the suboxide is a chromium suboxide, and the oxide is a chromium oxide. Accordingly, the surface of the film is formed with minute irregularities, and adhesion of the secondary film can be improved.

According to a fifth aspect of the invention, the primary film is softer than metal chromium and has insulation properties and corrosion resistance. Accordingly, the primary film, which is lighter than metal chromium, has an improved workability, insulation properties and corrosion resistance.

A sixth aspect of the invention includes a thin secondary film formed on the surface with the irregularities of the primary film. Accordingly, the secondary film is formed on the primary film having a porous structure firmly and rigidly, preventing the secondary film from peeling and cracking. Further, workability of the work after the secondary film is formed can be improved.

A seventh aspect of the invention includes an impregnation layer formed by the secondary film on a surface layer of the primary film. Accordingly, the primary film is integral with the secondary film, preventing the secondary film from peeling and cracking. The porous structure of the primary film enables the secondary film to be adhered firmly and rigidly.

According to an eighth aspect of the invention, fine particles or crystals of the secondary film are disposed on the irregularities of the primary film independently and with high density. Accordingly, when a stress is applied to a part of the fine particles and crystals of the secondary film, the rest of the fine particles and crystals is not affected. Thus, when the work is bent or the surface of the secondary film is damaged after formation of the secondary film, peeling or cracking of the secondary film does not occur. The workability of the work is improved and thus various processing techniques can be applied to the work.

According to a ninth aspect of the invention, the primary film has a thickness of 1 μm or more and the secondary film has a thickness of 5 μm or more. Accordingly, the thinner primary and secondary films are formed. When the secondary film such as a coating is formed, the primary film functions rationally instead of the conventional primers. Additionally, by forming a thinner secondary film, less paint is used, for example, the secondary film such as a coating can be formed rationally and at low cost.

According to a tenth aspect of the invention, the secondary film includes any one of a polymer material, an inorganic or organic paint coating, a functional material, or ceramics. Accordingly, various materials can be used for the secondary film.

According to an eleventh aspect of the invention, the work is any one of stainless steel, nickel, iron, copper, aluminum, brass, other metals, alloy, synthetic resin, glass, ceramics, paper, fiber, or wood. Accordingly, various materials can be used.

According to a twelfth aspect of the invention includes placing the work and an anode piece in a bath for receiving a treatment liquid: applying positive and negative voltages for the work and the anode piece; adjusting a bath temperature of the treatment liquid to low temperature; and depositing a thin and porous primary film formed by a suboxide or an oxide containing metal ions in the treatment liquid on the work by electrochemical action, or depositing a thin and porous primary film formed by a suboxide or an oxide containing metal ions in the treatment liquid in an electroless bath on the work by chemical reaction. Accordingly, in the case of the electrochemical action, deposition of the suboxide or oxide on the work is promoted, deposition of metal chromium is inhibited, and thus making the suboxide or oxide softer than the metal chromium. Further, the primary film is formed on the surface layer of the work firmly and rigidly and prevented from peeling and cracking, and thus the workability is improved. In the case of the chemical reaction, the primary film is formed more easily with simple facilities compared with a case of electrochemical action.

According to a thirteenth aspect of the invention, the treatment liquid of the electrochemical action includes chromic anhydride and a reduction inhibitor. Accordingly, dispersion of chromate is achieved during electrolysis of the treatment liquid, while a current which passes through the work is inhibited, and thus deposition of metal chromium can be inhibited and the conductivity and the hardness of the primary film can be inhibited.

According to a fourteenth aspect of the invention, the treatment liquid of the chemical action includes an agent for supplying metal ions, a reducing agent, and an additive such as ceramics. Accordingly, deposition of the additive such as ceramics, which is the suboxide or oxide, is promoted.

According to a fifteenth aspect of the invention, a bath temperature of the treatment liquid of the electrochemical action is adjusted to 10° C. or less. Accordingly, deposition of the primary film is promoted and deposition of the metal chromium is inhibited, and thereby enabling to promote deposition of the chromium suboxide.

A sixteenth aspect of the invention includes a thin secondary film, wherein the secondary film is attached to or adsorbed on the primary film, or the secondary film is formed by impregnation or firing. Accordingly, the secondary film such as a coating can be formed firmly and rigidly on the porous primary film.

According to a seventeenth aspect of the invention, the secondary film includes any one of a polymer material, an inorganic or organic paint coating, a functional material, or ceramics, and any one of the above is applied, sprayed, or baked on the primary film, or the work including the primary film is immersed into one of the materials above described, or applying a voltage or an electric field to the work including the paint and the primary film, or the ceramics are fired.

Accordingly, the secondary film of the above materials is attached to or adsorbed on the primary film, or the secondary film is formed by impregnation or firing. Additionally, the secondary film of the materials above is formed in the optimum manner.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing a state in which the primary film is deposited on the work by electrochemical action applied to the present invention.

FIG. 2 is an explanatory view showing a state in which a coating which is the secondary film is formed on the primary film of the work by a spraying method applied to the present invention.

FIG. 3 is micrographic images showing the surface states of chromium suboxide or the primary film deposited by adjusting the bath temperature to −5° C. in a deposition process of the primary film by the electrochemical action applied to the present invention. The images are shown with magnification at different time periods after deposition.

FIG. 4 is micrographic images showing the surface states of chromium suboxide or the primary film deposited by adjusting the bath temperature to 15° C. in a deposition process of the primary film by the electrochemical action applied to the present invention. The images are shown with magnification at different time periods after deposition.

FIG. 5 is a magnified micrographic image showing a deposition state after 20 minutes have passed in the deposition of the chromium suboxide in FIG. 3.

FIG. 6 is a magnified micrographic image showing a deposition state after 20 minutes have passed in the deposition of the chromium suboxide in FIG. 4.

FIG. 7 is scanning-micrographic images, with gradual magnification, showing a deposition state of the chromium suboxide in FIG. 3.

FIG. 8 is micrographic images, with gradual magnification, showing a cross section of the deposition state of the chromium suboxide.

FIG. 9 is a cross-sectional view schematically showing a state of impregnation when the suboxide which is the primary film is deposited on the surface of the work.

FIG. 10(a) and FIG. 10(b) are explanatory views of the enlarged main parts in FIG. 9 and show the work with different surface states.

FIG. 11 is a magnified micrographic image of the main part in FIG. 9.

FIG. 12 is a cross-sectional view schematically showing a state of forming a coating which is the secondary film after deposition of the suboxide which is the primary film on the surface of the work.

FIG. 13 is an enlarged explanatory view of the main part in FIG. 12. The surface of the primary film functions like a chopstick holder, and the secondary film is embedded in the holes for supporting chopsticks.

FIG. 14 is an enlarged cross-sectional view showing a state of a coating which is the conventional secondary film being formed.

FIG. 15 is an enlarged cross-sectional view schematically showing the work being bent after formation of the secondary film.

FIG. 16 is an enlarged schematic view of the bent portion of the work in FIG. 15.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention, applied to a surface treatment in which a primary film is formed on the surface of a work or component to be treated made of stainless steel plate and then a secondary film is formed on the primary film, will now be described below with reference to the drawings. In FIGS. 1 through 16, reference numeral 1 is a bath, which receives a treatment liquid 2 or electrolyte therein.

The treatment liquid 2 has the same structure as a black chrome bath and the composition of 300 to 400 g/l of chromic anhydride CrO₃, 5 to 10 g/l of sodium silicofluoride NaSiF₆, and 2 to 5 g/l of barium acetate C₄H₆O₄Ba. The bath temperature of the treatment liquid 2 is adjusted to 10° C. or below by using a cooling apparatus, described later, to promote deposition of the suboxide of chromium suboxide CrO₃ on the surface of the work 3 and to inhibit deposition of metal chromium Cr.

In this case, in order to deposit a predetermined suboxide, the bath temperature should preferably be 0° C. or below such that the treatment liquid 2 does not freeze. In some embodiments, the temperature is adjusted from −5 to 10° C.

The work 3 which is a cathode piece 3, a metal chromium or an anode piece 4 which is a soluble electrode, and a carbon or lead which is an insoluble electrode are soaked and placed in the treatment liquid 2. Wiring 5, 6 for applying a positive and negative voltage are connected to the above components. A voltage is applied from a power unit 8 via a controller unit 7 having a function of rectification. These units control the current density of the work 3 and the anode piece 4 to 20 A/dm².

In some embodiments, a stainless steel plate (SUS304) having a thickness of 0.5 mm is used as the work 3, but the work may not be limited to a metal piece and may be any one of nickel, iron, copper, aluminum, brass, other metals, alloy, synthetic resin, glass, ceramics, paper, fiber, or wood on which an oxide may be deposited.

A cooling bath 9 for receiving a predetermined amount of the treatment liquid 2 is placed in the peripheral position of the bath 1, and a zigzag or coil-like refrigerant pipe 11 of the cooling apparatus 10 is provided in the cooling bath 9.

In drawings, reference numeral 12 is a compressor for circulating a refrigerant provided in a cooling circuit of the cooling apparatus 10, reference numeral 13 denotes a cooling cylinder for storing the cooling bath 9, and reference numeral 14 is a filter provided inserted in a drain passage at the lower end of the cooling bath 9.

A treatment-liquid introduction pipe 15 is provided at the upper position of the cooling bath 9 and a treatment-liquid discharge pipe 16 is provided at the lower part of the cooling bath 9. One end of the treatment-liquid introduction pipe 15 is provided submerged into the treatment liquid 2 in the bath 1, and a liquid feed pump 17 for sucking the treatment liquid 2 is provided inserted in the treatment-liquid introduction pipe 15. Further, the treatment-liquid discharge pipe 16 has one end connected to the filter 14 and the other end connected to the lower part of the bath 1 via a check valve 18.

FIG. 2 is a state in which the suboxide which is the primary film is deposited on the work 3 and then a coating is formed by spraying a paint which is the secondary film on the primary film. Reference numeral 19 denotes a small coating gun used for spraying. The coating gun 19 includes a cylindrical paint tank 20 provided to stand obliquely at the side of the nozzle of the coating gun 19 and a compressed-air duct 21 connected to the lower part of the coating gun 19.

Then, a synthetic-resin paint in the paint tank 20 may be sprayed on the primary film 23 deposited on the work 3 via an operation of a trigger 22. In some embodiments, chromium suboxide CrO₃ is deposited on the work 3 as the suboxide which is the primary film 23.

The other methods for forming the coating which is the secondary film include: applying with a brush or roller; a baking finish technique in which a paint is heated and hardened; an immersion coating technique in which the work 3 with the primary film is immersed in the paint; an electrodeposition coating technique in which the work 3 in a water paint is coated by applying static electricity of opposite polarity; and an electrostatic coating technique in which a coating is electrically adsorbed on the work 3 by charging the work 3 and a spray-form paint with opposite polarity. The optimum technique may be selected according to the working conditions.

Next, in the method of the present invention, the suboxide which is the primary film 23, or chromium oxide Cr₂O₃ which is the oxide of the suboxide is firstly deposited on the work 3. Then the coating which is the secondary film 24 is formed on the primary film 23.

When the suboxide which is the primary film 23, or chromium oxide Cr₂O₃ which is the oxide of the suboxide is firstly deposited on the work 3 and then a coating which is the secondary film 24 is formed on the primary film 23, the bath 1 for receiving the treatment liquid 2, the work 3 which is a cathode piece, and the anode piece 4 is prepared and then a predetermined voltage is applied to the work 3 and the anode piece 4. The power unit 8 which acts on a predetermined current density and the controller unit 7 for controlling the power unit 8 are mounted on the above components. Further, the cooling bath 9 is placed at the close position of the bath 1.

The cooling bath 9 is equipped with the cooling apparatus 10 and the refrigerant pipe 11 is provided in the cooling bath 9. The treatment-liquid introduction pipe 15 is provided at the upper position of the cooling bath 9 and the treatment-liquid discharge pipe 16 is provided at the lower part of the cooling bath 9. The liquid feed pump 17 is provided inserted in the treatment-liquid introduction pipe 15. One end of the treatment-liquid introduction pipe 15 is provided in the treatment liquid 2 in the bath 1, and one end of the treatment-liquid discharge pipe 16 is connected to the lower part of the bath 1 via the check valve 18.

The treatment liquid 2 is then prepared. The treatment liquid 2 has the composition of 300 to 400 g/l of chromic anhydride CrO₃, 5 to 10 g/l of sodium silicofluoride NaSiF₆ which is a reduction inhibitor, and 2 to 5 g/l of barium acetate C₄H₆O₄Ba, and the treatment liquid 2 is received in the bath 1.

In this case, sodium silicofluoride and barium acetate in the treatment liquid 2 inhibit a flow of electricity, inhibiting deposition of metal chromium Cr on the surface of the work 3 and promoting deposition of chromium suboxide CrO₃ which is the suboxide.

The work 3 and the anode piece 4 are received in the bath 1, the wiring 5, 6 thereof are connected to the controller unit 7 and the power unit 8. The power unit 8 is turned on to apply a predetermined voltage, and the current density of the work 3 and the anode piece 4 is adjusted via the controller unit 7. In some embodiments, the current density of the work 3 and the anode piece 4 is adjusted to 20 A/dm.

Then, the liquid feed pump 17 is started to suck the treatment liquid 2 in the bath 1 and the treatment liquid 2 sucked is sent to the cooling bath 9. Further, the cooling apparatus 10 is started to drive the compressor 12 and circulate the refrigerant to the refrigerant pipe 11. The treatment liquid 2 in the cooling bath 9 is then cooled and sent to the lower part of the bath 1 from the treatment-liquid discharge pipe 16.

Thus, the treatment liquid 2 in the bath 1 is cooled and, in some embodiments, the bath temperature is adjusted to 10° C. or below. In this case, in order to deposit a predetermined suboxide, the bath temperature should preferably be 0° C. or below such that the treatment liquid 2 does not freeze. In some embodiments, the temperature is adjusted from −5 to 10° C.

When a voltage is applied to the work 3 and the anode piece 4, hydrogen gas is generated on the side of the work 3 and moved up in the treatment liquid 2 and then released into the air, while oxygen gas is generated on the side of the anode piece 4 and moved up in the treatment liquid 2 and then released into the air.

Chromic anhydride which is the main component of treatment liquid 2 is ionized at the anode 4, and the chromate ions are separated from the anode piece 4. The separated chromate ions move and disperse in the treatment liquid 2 and move toward the interface of the work 3. Then the chromate ions are reduced to trivalent chromium. The trivalent chromium is deposited on the interface of the work 3.

At that time, trivalent chromium is deposited on the interface of the work 3 based on the metal Cr. The deposited metal Cr is coupled with chromium suboxide CrO₃ which is the suboxide 23, and then the metal Cr and chromium suboxide are attached thereon in sequence to form a suboxide film. When the thickness of the film reaches 1 to 2 μm, conductivity of the suboxide film is lost and formation of the suboxide stops.

The chromium suboxide film is semibright black and a thin film with a thickness of 1 to 2 μm. Thereafter, the chromium suboxide film is combined with oxygen in the air and changed into an oxide of Cr₂O₃, and making the primary film more rigid.

In deposition of the suboxide film, the bath temperature is adjusted to low temperature which is 10° C. or below. In some embodiments, the temperature is adjusted to −5 to 10° C. The current is inhibited by sodium silicofluoride and barium acetate in the treatment liquid 2. Further, since the current density of the work 3 and the anode piece 4 is set to 20 A/dm², deposition of metal chromium Cr on the work 3 can be inhibited.

Thus, the primary film 23 made of the suboxide is presumed to be softer than the metal Cr and have a lower conductivity.

The inventors checked the components of the deposited suboxide film by quantitative analysis using an Electron Probe Micro Analyzer (EPMA 1720) of SHIMADZU CORPORATION. The following data was obtained: C: 24.91%; O: 18.82%; Si: 35.75%; Cr: 11.16%; and Ni: 9.36%. This data shows deposition of Cr is inhibited.

Next, the inventors checked the surface state of the primary film 23 by using a super resolution field emission type scanning electron microscope (SU-10) of Hitachi High-Technologies Corporation. The results shown in FIGS. 3 and 4 were obtained.

FIG. 3 is photograph images of the surface states after 5 minutes, 10 minutes, and 20 minutes from the initiation of deposition of the suboxide which is the primary film 23 at the bath temperature of −5° C. and the current density of 20 A/dm², with magnification of 10K, 20K, 50K, and 100K (K: ×1000). Plural masses or granular structures appear on each state, and these structures grow as time passes from the deposition and clearances thereof also increase. It was observed that irregularities were distributed and clearly formed.

FIG. 4 is photograph images of the surface states after 5 minutes, 10 minutes, and 20 minutes from the initiation of deposition of the suboxide which is the primary film 23 at the bath temperature of 15° C. and the current density of 20 A/dm², with magnification of 10K, 20K, 50K, and 100K. Plural grains or scale-like structures appear on each state, and these structures increase and grow as time passes from the deposition and clearances thereof also increase. Thus, distribution of irregularities was observed.

FIG. 5 is a photograph image of the surface state after 20 minutes from the initiation of deposition of the primary film 23 at the bath temperature of −5° C., with a magnification of 100K. The size of the masses or granular structures are shown with a reference scale for comparison. The masses or granular structures with the size of 25 to 200 nm were observed.

FIG. 6 is a photograph image of the surface state after 20 minutes from the initiation of deposition of the suboxide at the bath temperature of 15° C., with magnification of 100K. The size of the structures of grains or folds is shown with a reference scale for comparison. The structures of grains or folds with the width of 25 to 50 nm and the length of 400 to 650 nm were observed.

Additionally, FIG. 7 includes photograph images of the surface state of FIG. 5, taken by a scanning microscope, with a magnification of 10 to 50K. It was observed that the suboxide film had a fine-porous structure, the surface was formed like a cake with minute irregularities or sponge, and the surface had many irregularities with the size of 50 to 200 nm.

FIG. 8 is a photograph image of a cross section of the suboxide or the primary film 23 in FIG. 3. It was observed that minute irregularities were formed on the surface of the primary film 23 to cover the surface of the work 3.

As seen from the above, the surface of the work 3 may be represented schematically as shown in FIG. 9. As shown in FIG. 10(a) and FIG. 10(b), further enlarged images of FIG. 9, since various irregularities and serrations on the surface of the work 3 are engaged with the irregularities of the porous primary film 23, the primary film 23 seems to be adhered and deposited on the work 3 closely.

This state is further enlarged and shown in FIG. 11. The primary film 23 is arranged in a stripe pattern with predetermined intervals and engaged with the surface layer of the work 3 so that the primary film 23 is adhered to the work 3 firmly.

Thus, an impregnation layer made of the primary film 23 is formed on the surface of the work 3 so that the work 3 is integral with the primary film 23. Accordingly, the primary film 23 is adhered to the surface layer of the work 3 rigidly and closely, preventing the primary film 23 from peeling and cracking. Further, the secondary film 24 is formed on the porous structure of the primary film 23 firmly and rigidly so that peeling of the secondary film 24 is prevented.

Next, in forming a coating which is the secondary film 24 on the work 3, inorganic or organic paint coating is applied or adsorbed onto the suboxide or oxide deposited on the work 3.

In some embodiments, a spraying method of coating with the coating gun 19 is adopted as an applying or adsorbing method of the coating, but other techniques may also be adopted.

In this cases, since oxygen may penetrate the coating, the coating may be formed immediately after formation of the primary film 23 or formed later on. The coating only needs to be formed on the rigid oxide in the end. Thus, the timing of the coating formation does not affect the quality.

Then, the surface of the suboxide or oxide of the primary film 23 deposited on the work 3 before forming the coating is cleaned and dried. The work 3 is suspended on, for example, an appropriate jig 25.

Then a desired paint is filled in the paint tank 20 of the coating gun 19. By holding the coating gun 19 connected with the compressed-air duct 21, the paint is sprayed via an operation of the trigger 22, aiming the nozzle toward the work 3. This state is shown in FIG. 2.

The paint applied to the work 3 in a manner as described above is attached to the surface of the primary film 23 of the suboxide or oxide, and then heated and hardened. In this case, the forming state of the coating which is the secondary film 24 is shown in FIGS. 12 and 13.

In forming of the secondary film 24 of the present invention, the thin primary film 23 which the suboxide or oxide deposited on the work 3 is used instead of primers that have been frequently used for conventional coating. Every fine particle or crystal of the coating is disposed on the primary film 23 independently and with high density.

At that time, the coating needs to be formed basically only once, and primer, middle, and top coatings, that are required in the conventional manner and time-consuming, are unnecessary. The film is formed in a thin film having a thickness of 5 μm, which is one-fifth to one-third of the conventional ones. The thin film is engaged with the minute irregularities of the primary film 23 to be adhered closely. Thus, the amount of the paint used is reduced and the coating is formed readily compared with the conventional coating method, and whereby the coating is formed rationally and at low cost.

In this case, due to the porous structure of the primary film 23, the plural irregularities or holes of the surface function like a chopstick holder, and a coating which is the secondary film 24 is fitted and embedded in the holes. Accordingly, the density of embedded coating can also be adjusted by the holes, polymer chains of the synthetic resin coating can be adjusted, and thereby distributing the secondary film 24 with high density and attaching the secondary film 24 firmly onto the irregularities and holes.

An impregnation layer of the secondary film 24 is formed on the surface layer of the primary film 23. Since the secondary film 24 is integral with the primary film 23, the secondary film 24 is prevented from peeling. The porous structure of the primary film makes the secondary film to be adhered firmly and rigidly.

As described above, the present invention includes impregnation of the work 3 and the primary film 23, and impregnation of the primary film 23 and the secondary film 24, and thereby promoting integration thereof. Accordingly, they are adhered firmly and rigidly. Further, peeling and cracking when the primary film 23 and secondary film 24 are bent are prevented.

Additionally, the suboxide or oxide has insulation properties so that a current does not pass through the work 3 via the suboxide or oxide even when the coating is made thinner. As a result, corrosion due to potential difference does not occur, and thereby improving corrosion resistance.

Since primary film 23 is porous and soft, the fine particles of the coating easily enter and are engaged with the work 3, and disengagement from the work 3 is prevented. The film is reliably embedded and functions like an anchor component so that the coating is formed firmly and rigidly. Connection with other coating applied thereon is also promoted to form the coating rationally.

As described above, grains and crystals of the coating are respectively disposed independently and with high density. Accordingly, when a stress is applied to a part of the grains and crystals, the rest of the grains and crystals is not affected. Thus, when the work 3 is bent as shown in FIGS. 15 and 16 after formation of the coating, the stress is dispersed. Further, peeling or cracking of the coating when the surface of the coating is damaged does not occur.

Thus, the work 3 with the coating formed thereon has a good workability, and various processing techniques can be applied to the work 3. The surface of the coating was cut in a lattice pattern, and peeling of a cross-cut piece was tested. No peeling was observed and the coating with high adhesion was observed.

On the other hand, FIG. 14 shows a state of a conventional coating 27 being formed. The grains and crystals of the coating 27 are disposed loosely and with low density. To prevent corrosion caused by potential difference, such as pinholes, a very thick coating having a thickness of, for example, 50 to 100 μm, is required. Such coating is formed by applying the primer 26 to the work 3 and then applying the coating 27 in layers.

The above coating process requires labor and the amount of paint used also increases, whereby the working cost also increases. As described above, the grains and crystals of the coating are not independent and loosely disposed at low density, so that when a stress is applied to a part of the grains and crystals, it has impacts on the rest of the grains and crystals. When the work 3 is bent or the surface of the coating is damaged after formation of the coating, the coating 27 peels off and cracks, leading to a poor workability.

In the above embodiment, an electroplating technique based on the electrochemical action is adopted as a deposition method of the primary film 23 on the work 3. Other deposition techniques that can be applied include an electroless plating. If additives such as nickel sulfate which is an agent for supplying metal ions, sodium hypophosphite which is an reducing agent, and powder ceramics are added in the composition of the treatment liquid 2 in the electroless bath, deposition of the suboxide or oxide, or ceramics can be promoted by using simple equipment compared with the equipment for electrochemical action.

In the above embodiment, the secondary film 24 is used as a coating, but a functional material, ceramics, Teflon (registered trademark), or fluorine may be used instead of the coating.

The functional materials include, for example, a polymer material, difluoride material, tetrafluoride material, fluorine compound, titanium dioxide, zinc oxide, manganese dioxide, alumina, bentonite, hydroxyapatite, zeolite, talc, collinite, porous silica, gold, platinum, palladium, boron nitride, titanium nitride, aluminum nitride, DLC, magnetic material, metallic material, and carbon material. They may be used on the surface and the interface of the primary film 23 or intervened inside the primary film 23 for improving functionalities of the primary and secondary films 23, 24, such as corrosion resistance, adsorptive properties, abrasion resistance, catalytic properties, thermal conductivity, low friction properties, and antibiotic properties.

As described above, respective fine particles and crystals of the coating are disposed independently and with high density on the primary film 23 of the suboxide or oxide deposited on the work 3. The film is formed in a thin film having a thickness of one-fifth to one-third of the conventional ones. The fine particles and crystals are adhered to the minute irregularities on the surface of the primary film 23 closely and firmly.

Thus, if a stress is applied to a part of the fine particles and crystals of the coating which is the secondary film 24, the rest of the fine particles and crystals are not affected, resulting in improving workability of the work 3 after formation of the coating.

INDUSTRIAL APPLICABILITY

The present invention is suitable for a film-forming structure and a film-forming method on a work that include closely depositing a thin primary film on a work, the primary film being a suboxide or an oxide which is soft and has insulation properties and corrosion resistance. The work is integrated with the primary film to prevent the primary film from peeling, and thereby improving the workability. The thin secondary film such as a coating is attached to the primary film closely, thereby reducing the amount of paint used. The primary film is integrated with the secondary film to prevent the secondary film from peeling, improving the workability after formation of the secondary film, and thereby forming the primary and secondary films rationally.

REFERENCE SIGNS LIST

-   1 bath -   2 treatment liquid -   3 work (cathode piece) -   4 anode piece -   23 primary film (suboxide, oxide) -   24 secondary film (coating) 

1. A film-forming structure on a work comprising: a work having a surface on which a film is formed; and a thin primary film formed by a suboxide or an oxide comprising metal, deposited on the surface of the work, and wherein the primary film is a porous film.
 2. The film-forming structure on the work according to claim 1, further comprising an impregnation layer formed by the primary film on the surface of the work.
 3. The film-forming structure on the work according to claim 1, wherein the primary film has a surface having minute irregularities.
 4. The film-forming structure on the work according to claim 1, wherein the suboxide is a chromium suboxide, and the oxide is a chromium oxide.
 5. The film-forming structure on the work according to claim 1, wherein the primary film is softer than metal chromium and has insulation properties and corrosion resistance.
 6. The film-forming structure on the work according to claim 3, further comprising a thin secondary film formed on the surface with the irregularities of the primary film.
 7. The film-forming structure on the work according to claim 6, further comprising an impregnation layer formed by the secondary film on a surface layer of the primary film.
 8. The film-forming structure on the work according to claim 6, wherein fine particles or crystals of the secondary film are disposed on the irregularities of the primary film independently and with high density.
 9. The film-forming structure on the work according to claim 6, wherein the primary film has a thickness of 1 μm or more and the secondary film has a thickness of 5 μm or more.
 10. The film-forming structure on the work according to claim 6, wherein the secondary film comprises any one of a polymer material, an inorganic or organic paint coating, a functional material, or ceramics.
 11. The film-forming structure on the work according to claim 1, wherein the work is any one of stainless steel, nickel, iron, copper, aluminum, brass, other metals, alloy, synthetic resin, glass, ceramics, paper, fiber, or wood.
 12. A film-forming method on a work for forming a film on a surface of a work comprising: placing the work and an anode piece in a bath for receiving a treatment liquid; applying positive and negative voltages for the work and the anode piece; adjusting a bath temperature of the treatment liquid to low temperature; and depositing a thin and porous primary film formed by a suboxide or an oxide containing metal ions in the treatment liquid on the work by electrochemical action, or depositing a thin and porous primary film formed by a suboxide or an oxide containing metal ions in the treatment liquid in an electroless bath on the work by chemical reaction.
 13. The film-forming method on the work according to claim 12, wherein the treatment liquid of the electrochemical action comprises chromic anhydride and a reduction inhibitor.
 14. The film-forming method on the work according to claim 12, wherein the treatment liquid of the chemical action comprises an agent for supplying metal ions, a reducing agent, and an additive such as ceramics.
 15. The film-forming method on the work according to claim 12, wherein a bath temperature of the treatment liquid of the electrochemical action is adjusted to 10° C. or less.
 16. The film-forming method on the work according to claim 12, further comprising a thin secondary film, wherein the secondary film is attached to or adsorbed on the primary film, or the secondary film is formed by impregnation or firing.
 17. The film-forming method on the work according to claim 16, wherein the secondary film comprises any one of a polymer material, an inorganic or organic paint coating, a functional material, or ceramics, and any one of the polymer material, the inorganic or organic paint coating, the functional material, or the ceramics is applied, sprayed, or baked on the primary film, or the work comprising the primary film is immersed into one of materials above, or applying a voltage or an electric field on the work comprising the paint and the primary film, or the ceramics are fired. 